(1) Field of the Invention
The present invention relates to a method and an apparatus for layer short detection of an electric rotating machine and in particular relates to a method and an apparatus for layer short detection of an electric rotating machine suitable for detecting a layer short of a field winding in operation by measuring a magnetic flux generated from a field winding.
(2) Description of Related Art
In general, in the case where a layer short takes place in an electric rotating machine. The number of turns of a field winding decreases at the point where the short has taken place and therefore the generated magnetic field decreases at layer short point. Moreover, the waveform of magnetic field becomes asymmetric. Thus, electromagnetic force may get unbalanced to thereby cause a great amount of vibration. Moreover, the field winding may be abnormally heated to burn out other components.
The above described phenomena will take place due to the centrifugal force due to high-speed rotation of a rotor of an electric rotating machine in operation or otherwise a force generated by heat expansion of a field winding due to temperature rise. Therefore, a layer short is more frequently detected in operations.
A detection apparatus for detecting a layer short of a field winding of electric rotating machine in operation described in JP-A-5-76156, for example, includes a detector for detecting a magnetic field generated by a field winding; cables for transmitting a signal of the magnetic field detector; a device for pulling out the cable to the outside of an electric rotating machine; and appliances for measuring signal of the magnetic field detector.
Normally, a magnetic field detector is installed on the surface of a stator iron core facing a rotor to measure a magnetic field in a gap between the rotor and the stator iron core to thereby detect a layer short.